program create_files

    implicit none
    integer :: i, N = 5
    character(10) :: file_name

    do i = 1, N
        write (file_name, '(a,i0,a)') "vtk", i, ".dat"
        open (1, file=file_name, status="replace")
        ! do things ...
        close (1)
    end do

end program create_files
